JPH02208623A - High-density scanning device - Google Patents

Abstract

PURPOSE:To eliminate the curvature of field completely by providing two transparent parallel plates between a 1st image formation optical system and a rotary polygon mirror rotatably around axes at a different angle from the optical axis. CONSTITUTION:The two transparent parallel flat plates 8A and 8B are provided between the 1st image formation optical system 2 and rotary polygon mirror 3 rotatably around axes 9A and 9B at the different angle from the optical axis. Then the two parallel flat plates 8A and 8B are rotated in the opposite directions as a deflection scan is made. Therefore, an image formation position on a plane corresponding to the rotating direction of a light beam shifts according to the deflection scan to compensate the curvature of field caused by the deflection scanning. Consequently, the curvature of field in one scanning direction is corrected without causing a shift in optical axis nor affecting optical characteristics in any other scanning direction.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a high-density scanning device having a surface tilt correction function, and particularly to a high-density scanning device that can correct field curvature in the sub-scanning direction plane using a simple mechanism. The present invention relates to a density scanning device.

(Prior Art) There are two types of light beam scanning devices: a post-objective type that has a condenser lens in front of a deflector, and a pre-objective type that has a condenser lens after the deflector.

Then, the use of rotating polygon mirrors as deflectors increased,
It is the mainstream of optical beam scanning devices.

This is because it can meet the demand for faster scanning.

Incidentally, a light beam scanning device using a rotating polygon mirror as a deflector has the advantage of being able to perform high-speed scanning, but on the other hand, it causes surface tilt, so it is necessary to correct the surface tilt. For example, Japanese Unexamined Patent Application Publication No. 1983-1989 discloses surface tilt correction technology.
Publication No. 106618.

As disclosed in Japanese Unexamined Patent Publication No. 62-147421, it is common to perform surface tilt correction using lenses having different refractive powers in the main scanning direction and the sub-scanning direction.

[Problem to be solved by the invention]

By the way, in a light beam scanning device, it is difficult to form a clear image of the light beam on the surface over the entire scanning area, and field curvature is likely to occur.Therefore, in a post-object type device, the light source is deflected. For example, a proposal was made in JP-A-54-14 to similarly correct field curvature in both the main scanning and sub-scanning directions by moving in the optical axis direction along with scanning.
220, and in both pre-object and post-object types, main scanning and sub-object scanning are achieved by moving the collimating lens and condensing lens in the optical axis direction along with deflection scanning. For example, a proposal to correct field curvature in both scanning directions was made in JP-A-5
This has been done in Publication No. 8-57108.

However, a spherical lens is used as the lens,
Since the spherical lens has an astigmatism difference, the magnitude of field curvature differs between the main scanning direction and the sub-scanning direction. If you move the spherical lens or light source along the optical axis, the field curvature will be corrected in the same way in both the main scanning direction and the sub-scanning direction. This results in insufficient correction of field curvature.

In addition, scanning devices that use a rotating polygon mirror as a deflector and have a surface tilt correction function have lenses in the optical path that have different refractive powers in the main scanning direction and the sub-scanning direction (so-called anamorphic lenses). The degree of field curvature differs between the main scanning direction and the sub-scanning direction. Specifically, the curvature of field in the main scanning direction can be corrected to a negligible level and is hardly a problem, but the curvature of field in the sub-scanning direction is very large and cannot be ignored. If you try to correct the sub-scanning direction by appropriately moving the lens along the optical axis along with deflection scanning, the curvature of field in the sub-scanning direction can be reduced, but the curvature of field in the main scanning direction will increase instead. Become.

The present invention has been made in view of the above circumstances, and it is possible to adjust the curvature of field in the ° and - scanning directions independently of the curvature of field in the other scanning direction, thereby substantially reducing the curvature of field. It is an object of the present invention to provide a high-density scanning device having a surface tilt correction function that can be completely eliminated.

(Structure of the invention) [Means for solving problems] In order to solve the above problems, the present invention provides a light source.

a first imaging optical system that forms a linear image of the light beam emitted from this light source; a rotating polygon mirror that deflects the light beam that is emitted from this first imaging optical system; It is disposed between a scanned medium scanned by a light beam and the rotating polygon mirror, and forms an image of the deflected light beam on the scanned medium, and also forms an image of the deflected light beam in a plane perpendicular to the deflection plane of the rotary polygon mirror. In a high-density scanning device including a second imaging optical system that makes a deflection surface and the medium to be scanned in a substantially conjugate relationship in terms of geometrical optics, a The device is characterized in that two transparent parallel flat plates are rotatably provided around an axis at a different angle from the optical axis.

[For production]

According to the present invention, since the two parallel plates are rotated in opposite directions of rotation as the deflection scans, the imaging position of the light beam on the plane corresponding to the rotation direction changes as the deflection scans, Field curvature due to deflection scanning can be corrected. In other words, when a light beam passes through a parallel plate, an optical delay occurs in the light beam, but the amount of optical delay changes depending on the direction of the parallel plate with respect to the optical axis, so the amount of optical delay is changed by rotating the parallel plate. By doing so, the imaging position can be corrected. Moreover, when the parallel plate is rotated around an axis perpendicular to the optical axis, for example, in the horizontal direction, the amount of optical delay changes only in the vertical direction.
A change in the imaging position occurs.

In the horizontal direction (lateral direction), changes in the amount of optical delay,
No change in imaging position occurs. Therefore, in one scanning direction,
For example, the curvature of field in the sub-scanning direction can be corrected completely independently of the curvature of field in the other scanning direction, eg, the main scanning direction.

Furthermore, since there are two parallel plates, by rotating them in opposite directions, the optical axis shift caused by one parallel plate can be corrected by the other parallel plate. Therefore, according to the present invention, only the curvature of field in one scanning direction can be corrected without any deviation of the optical axis and without affecting the optical characteristics in other scanning directions.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to illustrated embodiments.

1 to 8 illustrate a first embodiment of the present invention, of which FIG. 1 is a perspective view showing the overall schematic structure of a high-density scanning device.

In FIG. 1, reference numeral 1 indicates a light source such as a laser or a light source device (hereinafter simply referred to as a "light source") consisting of a light source and an optical system that substantially parallelizes the light beam emitted from the light source; 2 indicates the light source 1;
3 is a rotating polygon mirror that reflects the light beam emitted from the first imaging optical system 2; 3A as the center, the deflection reflecting surfaces 4, 4 .・・・
・Reflects the luminous flux at. 5 is a single lens with a cylindrical surface on the rotating polygon mirror 3 side and a flat surface on the other side, 6 is a rotating polygon mirror 3
The single lens has a cylindrical surface on one side and a toric surface on the other side, and the single lenses 5 and 6 constitute a second imaging optical system. The second imaging optical system aims to form a point-like image on the surface of the scanned medium 7 by focusing the light beam deflected by the rotating polygon mirror 3 in the horizontal direction, and performs main scanning direction synthesis. It has a focal length f, the deflection reflection surface 4 of the rotating polygon mirror 3 and the scanned medium 7 are in a geometrically optically substantially conjugate relationship in the sub-scanning direction, and it has an imaging lateral magnification βS.

Here, a specific example of the second imaging optical system will be described in detail.

d,:10.966 f M=100 Fso,=54.7.2θ
Advantage = 67.8°, α = 601, R/ f M =
0.132. f s =22.698, βB −−4,
12 However, r1 to r4 are the radius of curvature in the main scanning direction of each surface when the surfaces are 1 to 4 in order from the rotating polygon mirror 3 side, ri
Similarly, '~r,' is the radius of curvature of each surface in the sub-scanning direction, d□, d is the wall thickness at the center of the single lens 5°6, and d
8 is the air distance at the center between the single lenses 5 and 6, n
n= is the refractive index of the single lenses 5 and 6 for light with a wavelength λ780 nm, FM is the combined focal length in the main scanning direction, FNO is the brightness in the main scanning direction, fs is the focal length in the sub-scanning direction, θ Δ is the deflection angle, α is the angle formed by the incident beam and the optical axis of the lens, and R is the radius of the inscribed circle of the rotating polygon mirror 3.

8A and 8B are two transparent parallel flat plates arranged between the cylindrical lens 2 and the rotating polygon mirror 3. The parallel plates 8A and 8B are configured to rotate at the same angle in opposite directions about axes 9A and 9B that are perpendicular to the optical axis and extend in the horizontal direction. Having the parallel flat plates 8A and 8B in this way is a feature of the high-density scanning device of the present invention.

FIGS. 2(a) and 2(b) are cross-sectional views in the sub-scanning direction of this high-density scanning device, and FIG. 2(a) shows two transparent parallel flat plates 8.
The state is shown when A and 8B are perpendicular to the optical axis, and the figure (b) shows two parallel flat plates 8A and 8B
shows the state when rotated at a certain angle in the opposite direction about the rotation axes 9A and 9B from the state shown in FIG.

In the state shown in FIG. 2(a), the focal position of the cylindrical lens 2 is located approximately on the deflection reflecting surface 4, and the imaging position is located approximately on the scanned medium 7. From this state, the two parallel flat plates 8A and 8B are rotated around the rotation axis 9A as shown in FIG.

When rotated about 9B, the linear image formed by the cylindrical lens 2 is displaced by ΔX toward the light source, and the imaged light is displaced from the scanned medium 7 toward the rotating polygon mirror 3 by ΔX'.

At this time, the relationship between ΔX and ΔX' is Δx' = βs3・ΔX (where βS is the above-mentioned imaging lateral magnification)
The relational expression holds true.

FIG. 3 is a diagram for explaining the reason why the displacement ΔX occurs due to the rotation of the parallel flat plate 8 at the linear imaging position described above.

In the figure, 8 is a parallel plate, d is the thickness of the parallel plate 8, n is the refractive index of the parallel plate 8, and C is the rotation center of the parallel plate 8 (it does not necessarily have to be on the optical axis). ), N
is the normal to the surface of the parallel plate 8, U is the angle of the normal N with respect to the optical axis, Z is the amount of light floating, Δy is the amount of axial deviation of the light, and D is the light emission point of the parallel plate 8.

When the parallel plate 8 is rotated so that the angle of its normal N with respect to the optical axis is U, the lifting amount Z is expressed by the following equation.

Z=d (1-(cosu/n-5xnu)
Further, the axis deviation amount Δy is expressed by the following equation.

Δy = d (1-(cosu/n-smu
) 5 inu Therefore, when the two parallel flat plates 8a and 8b are tilted at the same angle in opposite directions as shown in FIG. 2(b), the amount of deviation ΔX of linear imaging is expressed by the following equation. Δx=2 (Z-d (1-(1/n)>3) Then, the optical axis deviation amount Δy is canceled by the two parallel plates 8A and 8B and becomes O. In this way, the optical axis Since the amount of deviation becomes 0, it can be said that correction of field curvature in the sub-scanning direction can be performed by the parallel plates 8A and 8B without causing deviation of the optical axis.

Note that d(1-(1/
n)) is the amount of uplift when U=O°.

FIGS. 4(a) and 4(b) show the normal N of the parallel plates 8A and 8B.
The amount of deviation ΔX of linear imaging with respect to the inclination angle U with respect to the optical axis of
In the same figure (a), the refractive index n of the parallel plates 8A and 8B is 1.5, and the plate thickness d is 3 m as a parameter.
The characteristics when changing the length to m, 6m, and 9mm are shown in the same figure (b
) is 1 with the plate thickness d as Sow and the refractive index n as a parameter.
．． 5 From this figure, which shows the characteristics when changed to 1.71.9.

When the tilt angle U is 06, the deviation amount ΔX is 0, but the tilt angle U
It can be seen that as the plate thickness d increases, the deviation amount ΔX increases in a substantially parabolic manner, and the amount of change in the deviation amount ΔX increases as the plate thickness d increases and the refractive index n increases.

FIG. 5 shows the change in field curvature due to the deflection angle θ due to the second imaging optical system, where 11 shown with a broken line indicates the curvature of field in the main scanning direction, and 12 shown with a solid line shows the curve in the sub-scanning direction. This is a curve showing the field curvature of . As mentioned above, it is clear from this figure that the magnitude and manner of change of field curvature are different in the main scanning direction and the sub-scanning direction, and even though the field curvature in the main scanning direction is completely O, However, the curvature of field in the sub-scanning direction is large and therefore requires correction as it is so small that it can be practically ignored.

FIG. 6 shows the change in the correction amount ΔX required to correct the field curvature in the sub-scanning direction shown by the solid line 12 in FIG. 5, depending on the deflection angle θ. By changing the tilt angle U appropriately according to the change in the deflection angle θ (by changing ΔX as shown in Fig. 6), the curvature of field in the sub-scanning direction can be completely eliminated as shown in Fig. 7. It will disappear. What remains is only a very small curvature of field in the main scanning direction, which does not require correction, as shown by curve 16.

FIGS. 8(a) and 8(b) show a displacement mechanism that changes ΔX by rotating the parallel plates 8A and 8B.
) is a view seen from the direction of the rotation axis, and FIG. 2(b) is a perspective view thereof. This displacement mechanism brings rotating seats 13 and 14 of the same diameter, to which parallel plates 8A and 8B are attached, into contact (or meshing).
By rotating one rotating seat 13 by the drive shaft 15, the parallel plates 8A and 8B are rotated at the same angle in opposite directions.

In the above embodiment, the two parallel plates have the same refractive index and the same thickness. However, this is not the only option, and two parallel flat plates with different refractive indexes and different thicknesses may be used. Here, the two parallel flat plates 8A and 8B have different thicknesses d and d' and refraction. rate n, n
', the above-mentioned inclination angle U is no longer the same, and by rotating with inclination angles u and u' that satisfy the following equation, it is possible to obtain You can get the same effect.

d(1-(cosu/f11:■place'Vf) 5in
u −−d′(1−(cosu′/ n −mnu
5inu' = 0 Fig. 9 shows another embodiment of the present invention.

In this embodiment, the parallel plates 8A and 8B are arranged on an axis 10A in the vertical direction (sub-scanning direction) perpendicular to the optical axis.

By rotating around 10B, the curvature of field in the main scanning direction is corrected. In other words, the direction of the field curvature to be corrected can be changed by changing the direction of the rotation axis. Generally, the field curvature in the main scanning direction is relatively small, but due to special circumstances, the field curvature in the main scanning direction may be There may be cases where the surface curvature becomes large and requires correction, but in this case, the direction of the rotation axes of the parallel flat plates 8A, 8B may be set in the sub-scanning direction as shown in FIG.

By providing two sets of parallel flat plates 8A and 8B and changing the rotation axis of one set and the other set, the curvature of field in the main scanning direction and the sub-scanning direction can be corrected completely independently. can.

〔Effect of the invention〕

As described above, according to the present invention, two parallel flat plates are arranged between the first imaging optical system and the rotating polygon mirror so as to be rotatable about an axis at a different angle from the optical axis, and are used for deflection scanning. Since they are configured to rotate relative to each other, it is possible to correct the imaging position by changing the amount of optical delay caused by the parallel plate by deflection scanning, and therefore, it is possible to correct field curvature.

Moreover, what is corrected is the curvature of field in the direction perpendicular to the rotational axis of the parallel plate. Therefore, depending on the direction of the rotational axis of the parallel plate, the curvature of field in the sub-scanning direction can be corrected in any direction, for example, in the image in the main scanning direction. It can be adjusted independently of the surface curvature. Therefore, the way of curving in the main scanning direction and the sub-scanning direction,
Field curvatures of different sizes can be almost reliably corrected.

Even if a shift in the optical axis occurs due to parallel plates, there are two parallel plates and they are tilted at the same angle in opposite directions, so the shift in the optical axis due to one parallel plate is corrected by the other parallel plate. According to the present invention, no deviation of the optical axis occurs after all.

The curvature of field can be corrected extremely well without causing any deviation of the optical axis.

[Brief explanation of the drawing]

1 to 8 are for explaining one embodiment of the present invention, of which FIG. 1 is a perspective view showing the overall schematic configuration of a high-density scanning device, and FIG. (a) and (b) are cross-sectional views of the high-density scanning device in the sub-scanning direction, of which (a) shows the parallel plate perpendicular to the optical axis, and (b) shows the parallel plate in the vertical direction. Fig. 3 shows a state in which the plane is tilted from the state shown in Fig. 5(a), and Fig. 3 is a diagram illustrating the reason why the displacement ΔX occurs due to the rotation of the parallel plate of linear imaging.
Figures (a) and (b) are relationship diagrams between the inclination angle U of the parallel plate and the deviation amount ΔX of linear imaging, respectively.
(b) uses the refractive index as a parameter, and Fig. 5 shows the curvature of field and the deflection angle θ.
Figure 6 is a diagram showing the relationship between the displacement ΔX and the deflection angle θ, which corresponds to the amount of correction necessary to correct the field curvature shown in Figure 5, and Figure 7 is the image after correction. Figures 8(a) and 8(b), which are relationship diagrams between surface curvature and deflection angle θ, show a displacement mechanism for rotating a parallel plate. FIG. 9(b) is a perspective view, and FIG. 9 is a perspective view of a high-density scanning device showing another embodiment of the present invention. 1...Light source. 2... Cylindrical lens. 3...Rotating polygon mirror, 4...
Polarization reflecting surface, 5.6...Single lens, 7...Scanned medium, 8.8A, 8B...Parallel plate, 9A, 9B, I
OA, IOB...Axis, 13.14...
Rotating seat, 15... Drive wheel. Figure Figure Figure (a) Figure (a) Tilt angle □u (0) Tilt angle □u (') Figure (a) Figure

Claims (2)

[Claims] (1) A light source, a first imaging optical system that linearly images the light beam emitted from the light source, a rotating polygon mirror that deflects the light beam emitted from the first imaging optical system, and a rotating polygon mirror that deflects the light beam emitted from the first imaging optical system. Disposed between the rotating polygon mirror and a scanning medium that is scanned by a light beam deflected by a polygon mirror, the mirror forms an image of the deflected light beam on the scanning medium, and also forms an image of the deflected light beam on the scanning medium. A high-density scanning device including a second imaging optical system that makes the deflection surface and the scanned medium substantially conjugate in terms of geometrical optics in orthogonal planes, the first imaging optical system and the rotating polygon mirror. A high-density scanning device characterized in that two transparent parallel flat plates are rotatably provided between the two transparent parallel plates around an axis at a different angle from the optical axis. (2) Claim (1) characterized in that the two parallel flat plates are configured to rotate simultaneously and in opposite directions.
High density scanning device as described.